;;; org-git-link.el --- Provide org links to specific file version

;; Copyright (C) 2009-2014  Reimar Finken

;; Author: Reimar Finken <reimar.finken@gmx.de>
;; Keywords: files, calendar, hypermedia

;; This file is not part of GNU Emacs.

;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; This program is distaributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with this program.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; `org-git-link.el' defines two new link types. The `git' link
;; type is meant to be used in the typical scenario and mimics the
;; `file' link syntax as closely as possible. The `gitbare' link
;; type exists mostly for debugging reasons, but also allows e.g.
;; linking to files in a bare git repository for the experts.

;; * User friendy form
;;   [[git:/path/to/file::searchstring]]

;;   This form is the familiar from normal org file links
;;   including search options. However, its use is
;;   restricted to files in a working directory and does not
;;   handle bare repositories on purpose (see the bare form for
;;   that).

;;   The search string references a commit (a tree-ish in Git
;;   terminology). The two most useful types of search strings are

;;   - A symbolic ref name, usually a branch or tag name (e.g.
;;     master or nobelprize).
;;   - A ref followed by the suffix @ with a date specification
;;     enclosed in a brace pair (e.g. {yesterday}, {1 month 2
;;     weeks 3 days 1 hour 1 second ago} or {1979-02-26 18:30:00})
;;     to specify the value of the ref at a prior point in time
;;
;; * Bare git form
;;   [[gitbare:$GIT_DIR::$OBJECT]]
;;
;;    This is the more bare metal version, which gives the user most
;;    control. It directly translates to the git command
;;    git --no-pager --git-dir=$GIT_DIR show $OBJECT
;;    Using this version one can also view files from a bare git
;;    repository. For detailed information on how to specify an
;;    object, see the man page of `git-rev-parse' (section
;;    SPECIFYING REVISIONS). A specific blob (file) can be
;;    specified by a suffix clolon (:) followed by a path.

;;; Code:

(require 'org)
(defcustom org-git-program "git"
  "Name of the git executable used to follow git links."
  :type '(string)
  :group 'org)

;; org link functions
;; bare git link
(org-link-set-parameters "gitbare" :follow #'org-gitbare-open)

(defun org-gitbare-open (str)
  (let* ((strlist (org-git-split-string str))
         (gitdir (nth 0 strlist))
         (object (nth 1 strlist)))
    (org-git-open-file-internal gitdir object)))


(defun org-git-open-file-internal (gitdir object)
  (let* ((sha (org-git-blob-sha gitdir object))
         (tmpdir (concat temporary-file-directory "org-git-" sha))
         (filename (org-git-link-filename object))
         (tmpfile (expand-file-name filename tmpdir)))
    (unless (file-readable-p tmpfile)
      (make-directory tmpdir)
      (with-temp-file tmpfile
        (org-git-show gitdir object (current-buffer))))
    (org-open-file tmpfile)
    (set-buffer (get-file-buffer tmpfile))
    (setq buffer-read-only t)))

;; user friendly link
(org-link-set-parameters "git" :follow #'org-git-open :store #'org-git-store-link)

(defun org-git-open (str)
  (let* ((strlist (org-git-split-string str))
         (filepath (nth 0 strlist))
         (commit (nth 1 strlist))
         (line (nth 2 strlist))
         (dirlist (org-git-find-gitdir (file-truename filepath)))
         (gitdir (nth 0 dirlist))
         (relpath (nth 1 dirlist)))
    (org-git-open-file-internal gitdir (concat commit ":" relpath))
    (when line
      (save-restriction
	(widen)
	(goto-char (point-min))
	(forward-line (1- (string-to-number line)))))))


;; Utility functions (file names etc)

(defun org-git-split-dirpath (dirpath)
  "Given a directory name, return '(dirname basname)"
  (let ((dirname (file-name-directory (directory-file-name dirpath)))
        (basename (file-name-nondirectory (directory-file-name dirpath))))
    (list dirname basename)))

;; finding the git directory
(defun org-git-find-gitdir (path)
  "Given a file (not necessarily existing) file path, return the
  a pair (gitdir relpath), where gitdir is the path to the first
  .git subdirectory found updstream and relpath is the rest of
  the path. Example: (org-git-find-gitdir
  \"~/gitrepos/foo/bar.txt\") returns
  '(\"/home/user/gitrepos/.git\" \"foo/bar.txt\"). When not in a git repository, return nil."
  (let ((dir (expand-file-name (file-name-directory path)))
        (relpath (file-name-nondirectory path)))
    (catch 'toplevel
      (while (not (file-exists-p (expand-file-name ".git" dir)))
        (let ((dirlist (org-git-split-dirpath dir)))
          (when (string= (nth 1 dirlist) "") ; at top level
            (throw 'toplevel nil))
          (setq dir (nth 0 dirlist)
                relpath (concat (file-name-as-directory (nth 1 dirlist)) relpath))))
      (list (expand-file-name ".git" dir) relpath))))


(eval-and-compile
  (defalias 'org-git-gitrepos-p 'org-git-find-gitdir
    "Return non-nil if path is in git repository"))

;; splitting the link string

;; Both link open functions are called with a string of
;; consisting of three parts separated by a double colon (::).
(defun org-git-split-string (str)
  "Given a string of the form \"str1::str2::str3\", return a list of
  three substrings \'(\"str1\" \"str2\" \"str3\"). If there are less
than two double colons, str2 and/or str3 may be set the empty string."
  (let ((strlist (split-string str "::")))
    (cond ((= 1 (length strlist))
           (list (car strlist) "" ""))
          ((= 2 (length strlist))
           (append strlist (list "")))
          ((= 3 (length strlist))
           strlist)
          (t (error "org-git-split-string: only one or two :: allowed: %s" str)))))

;; finding the file name part of a commit
(defun org-git-link-filename (str)
  "Given an object description (see the man page of
  git-rev-parse), return the nondirectory part of the referenced
  filename, if it can be extracted. Otherwise, return a valid
  filename."
  (let* ((match (and (string-match "[^:]+$" str)
                     (match-string 0 str)))
         (filename (and match (file-name-nondirectory match)))) ;extract the final part without slash
    filename))

;; creating a link
(defun org-git-create-searchstring (branch timestring)
  (concat branch "@{" timestring "}"))


(defun org-git-create-git-link (file &optional line)
  "Create git link part to file at specific time"
  (interactive "FFile: ")
  (let* ((gitdir (nth 0 (org-git-find-gitdir (file-truename file))))
         (branchname (org-git-get-current-branch gitdir))
         (timestring (format-time-string "%Y-%m-%d" (current-time))))
    (concat "git:" file "::" (org-git-create-searchstring branchname timestring)
	    (if line (format "::%s" line) ""))))

(defun org-git-store-link ()
  "Store git link to current file."
  (when (buffer-file-name)
    (let ((file (abbreviate-file-name (buffer-file-name)))
	  (line (line-number-at-pos)))
      (when (org-git-gitrepos-p file)
	(org-store-link-props
	 :type "git"
	 :link (org-git-create-git-link file line))))))

(defun org-git-insert-link-interactively (file searchstring &optional description)
  (interactive "FFile: \nsSearch string: \nsDescription: ")
  (insert (org-make-link-string (concat "git:" file "::" searchstring) description)))

;; Calling git
(defun org-git-show (gitdir object buffer)
  "Show the output of git --git-dir=gitdir show object in buffer."
  (unless
      (zerop (call-process org-git-program nil buffer nil
                           "--no-pager" (concat "--git-dir=" gitdir) "show" object))
    (error "git error: %s " (with-current-buffer buffer (buffer-string)))))

(defun org-git-blob-sha (gitdir object)
  "Return sha of the referenced object"
    (with-temp-buffer
      (if (zerop (call-process org-git-program nil t nil
                               "--no-pager" (concat "--git-dir=" gitdir) "rev-parse" object))
          (buffer-substring (point-min) (1- (point-max))) ; to strip off final newline
        (error "git error: %s " (buffer-string)))))

(defun org-git-get-current-branch (gitdir)
  "Return the name of the current branch."
  (with-temp-buffer
    (if (not (zerop (call-process org-git-program nil t nil
                                  "--no-pager" (concat "--git-dir=" gitdir) "symbolic-ref" "-q" "HEAD")))
        (error "git error: %s " (buffer-string))
      (goto-char (point-min))
      (if (looking-at "^refs/heads/")   ; 11 characters
          (buffer-substring 12 (1- (point-max))))))) ; to strip off final newline

(provide 'org-git-link)

;;; org-git-link.el ends here